Depoling of single-domain bismuth titanate

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Abstract
Repeated c-axis switching of previously a-axis poled bismuth-titanate crystals generally results in a loss of the initial optical uniformity. Experimental results indicate that this optical degradation results from a recurrence of domains of opposite a-axis components in thin surface layers on both sides of the crystals. The cause of such depoling is not well understood, since the crystals are rather difficult to pole initially. A reasonable explanation may lie in the strain-relieving mechanism which involves strain both from c-axis domain switching and from initial crystal imperfections. This depoling is sharply reduced at low temperatures.Bismuth titanate has potential application to optically read memories and display devices. The depoling is not a serious problem for a read-only memory, for a write occasionally-read often memory, or for display and page-composer applications. However, for a pattern (and possibly for a holographic) read-write memory, the depoling may result in decreased read-out efficiency. Various methods for minimizing this problem are discussed.